DC-voltage vehicle electrical systems of motor vehicles are known that have a nominal voltage of 12V. Because of the multiplicity of users in DC-voltage vehicle electrical systems or, since users, such as perhaps servomotors of electrical steering systems have to be supplied, a nominal voltage of 12V is frequently not sufficient as energy supply. DC-voltage vehicle electrical systems of 42V are known that have a current source and users, and are developed as multi-voltage vehicle electrical systems. German Patent Application No. DE 101 19 985 describes a multi-voltage electrical system for a motor vehicle, having a first voltage level of 42V and a second voltage level of 14V. The first voltage level and the second voltage level are able to be connected via two parallel, switchable DC/DC converters. High performance users, such as the starter of the motor vehicle or the like, are connected to the first voltage level, a 42V branch of the multi-voltage electrical system, while the second voltage level, a 14V branch of the multi-voltage electrical system, is used to supply the usual users.
The DC/DC converters are able to be used in upwards and downwards operation, and are circuited in such a way that a external terminal point of the vehicle electrical system can be connected to a 42V-end terminal of the DC/DC converter. The switches of such 42V DC-voltage vehicle electrical systems should be provided by constructive measures with arc quenching devices. The power plug connections of such DC-voltage vehicle electrical systems should be disconnected, in order to avoid damage to their plug connectors when the plug is pulled out under load.